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A Complex dielectric constant -- metals, insulators and Reflections

  1. Aug 16, 2016 #1
    Hi everyone
    Can anyone help me understanding the physical meaning for the complex dielectric constant?
    Assuming a electromagnetic wave from air to a conductor, the following equation is valid
    R= ((n-1)2+k2)/((n+1)2+k2) where K is the extinction coefficient (the complex part of the complex refraction index)
    So, High K means high R
    K= ((ε12+ε22)1/2-ε1)1/2
    As far as i know, metals tend to exhibit high reflectivity due to high values of K, correct?
    And insulators in general, low values of K, also correct?
    So, according to some literature, the high values of K comes from high values of ε2. Also correct?
    And, to finish, where does the ε2 comes from, is it due to high free electrons density?
    Thank you very much for your time
  2. jcsd
  3. Aug 16, 2016 #2

    Andy Resnick

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    Allowing the dielectric constant/permittivity/permeability/etc. to be complex-valued is a way to model absorptive materials. Recall that an electromagnetic wave propagates through media with a phase term exp(ikz), so if k is complex-valued, the amplitude decreases exponentially with propagation distance.

    There are a few wrinkles to this- left handed materials, for example.
  4. Aug 16, 2016 #3
    And the complex part of these models comes from the absorption due to the high free electrons density?
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